Available collections. This is a mapping of strings onto sequences of nodes. The string represents the absolute URI of a resource. The sequence of nodes represents the result of the fn:collection function when that URI is supplied as the argument.

Available documents. This is a mapping of strings onto document nodes. The string represents the absolute URI of a resource. The document node is the root of a tree that represents that resource using the data model. The document node is returned by the fn:doc function when applied to that URI.

An axis step returns a sequence of nodes that are reachable from the context node via a specified axis. Such a step has two parts: an axis, which defines the "direction of movement" for the step, and a node test, which selects nodes based on their kind, name, and/or type annotation.

Boundary whitespace is a sequence of consecutive whitespace characters within the content of a direct element constructor, that is delimited at each end either by the start or end of the content, or by a DirectConstructor, or by an EnclosedExpr. For this purpose, characters generated by character references such as or by CdataSections are not considered to be whitespace characters.

A boundary-space declaration sets the boundary-space policy in the static context, overriding any implementation-defined default. Boundary-space policy controls whether boundary whitespace is preserved by element constructors during processing of the query.

Construction mode. The construction mode governs the behavior of element and document node constructors. If construction mode is preserve, the type of a constructed element node is xs:anyType, and all attribute and element nodes copied during node construction retain their original types. If construction mode is strip, the type of a constructed element node is xs:untyped; all element nodes copied during node construction receive the type xs:untyped, and all attribute nodes copied during node construction receive the type xs:untypedAtomic.

The constructor function for a given type is used to convert instances of other atomic types into the given type. The semantics of the constructor function call T($arg) are defined to be equivalent to the expression (($arg) cast as T?).